The earliest methods for the manufacturing of diamond required high temperatures and pressures. In the early 1980's it was discovered that diamond could be deposited by chemical vapor deposition (CVD) at a low pressure, approximately 0.1 atmosphere for example, Sho JP5927754 in 1983 and JP613320 in 1984, Kobashi U.S. Pat. No. 5,863,324 in 1999. The subsequently developed CVD methods all require the presence of flowing hydrogen gas containing a carbon-containing species such as methane (CH4), a hot tungsten filament or a plasma generator, and a nearby substrate held at high temperature, approximately 750 to 950° C. for high-quality diamond which is typically defined by Raman spectroscopy to have a well defined single sharp peak at 1332 cm−1 and diamond-like carbon, a completely different material, that have a distinctive broad band in the range of 1357 to 1580 cm−1 with a peak around 1555 cm−1. These CVD methods all suffer from several problems:
1. The deposition rate is low, typically on the order of 1 μm/h, causing the cost to be too high for many applications.
2. The flowing gas system requires gas supplies, control meters, a continuously operating vacuum pump, and often a plasma generator. The equipment is costly and the methods are wasteful of feed materials and electricity, all contributing to the high cost of CVD methods.
3. The high temperature required for the substrate leads to chemical reactions of the gas with some substrates. For example, attempted growth on materials containing iron, nickel or cobalt yields poor-quality, non-adhering diamond on top of porous graphite. To avoid such problems, buffer layers of different compositions must be used.
4. The high temperature required for deposition also leads to large stresses, which, in turn, caused delamination, warping, and cracking upon cooling to room temperature. This stress comes about primarily because the thermal contraction of diamond differs from that of the substrate, combined with the large temperature change upon cooling.
5. The high temperature required for deposition by CVD has also made it impossible to deposit diamond on many materials that would be destroyed by this temperature. This restriction included all polymeric materials, as well as many semiconductor and device structures.
6. Another approach to the problem in 5 is to use a two-step process wherein the CVD diamond is first deposited at temperatures above 800° C. and then removed, transferred and attached to the final substrate.
There is need for an improved method for manufacturing diamond coatings that will overcome the problems noted above to reduce cost, increase growth rate, reduce waste, reduce components, increase material quality, reduce stress on substrates and coatings, and create the opportunity to deposit on polymeric materials. The deposition of diamond by a chemical vapor transport method at low temperature and low pressure provides such coatings. Although the exceptional properties of diamond are well known, the present invention provides the first means to deposit diamond at low temperature and pressure. Additional applications hitherto not possible because of high deposition temperatures also suggest themselves; for example, the use of a diamond substrate in display devices and the fabrication of transistors made from diamond.